"Iron Dutchess" cost £130,000 alltogether About £28,000 for the steelwork, the rest on transporting it by road from Long Sutton in Licolnshire to Shardlow Marina in Derbyshire and subsequent fit out.
There is a full spec' sheet
here.It would be hard to give you a figure without the modifications as they began with changes to the steelwork during the shell build.
Also the figures above are 2003 prices, what the cost would be today I don't know.
Hope this helps.